A binder 10 includes a base 15 formed with through passages 14 that allow binding legs 13 to pass through respectively, movable members 16 which are mounted on this base 15 and located at positions corresponding to the through passages 14 respectively, and an operating section 17 which connects these movable members 16 to each other and operates the movable members 16. In one embodiment, the sensor is integrally formed with a reaction disc in the brake booster. In another aspect, an interference filter at the front facet provides spectral shaping.